The intramolecular cation radical Diels-Alder reaction, a heretofore unprecedented reaction, will be exemplified and its salient reaction characteristics established, including the scope, selectivities, and aspects of the reaction mechanism. As a consequence of the unusually mild conditions of the cation radical Diels-Alder reaction (0 to -50 C or even below for times as short as 2-5 min) and its phenomenally high endo selectivity in appropriate instances (not to mention virtually complete stereospecificity, regiospecificity, and chemoselectivity) the new reaction is confidently expected to offer expedient solutions to many of the most urgent limitations of the thermal intramolecular Diels-Alder. These include sigmatropic rearrangements, which often complicate or frustrate thermal additions to cyclic dienes, and the variable and often relatively low stereoselectivity with which the new ring juncture is frequently formed. These studies are foreseen as making feasible an exceedingly efficient synthesis of longifolene which, because of the sigmatropic shift problem, eluded earlier investigators. An efficient construction of the steroid nucleus will then be executed in order to further illustrate the utility and power of the new reaction.